Moons of Jupiter
Jupiter has 63 confirmed moons, giving it the largest retinue of moons with "reasonably secure" orbits of any planet in the Solar System. The most massive of them, the four Galilean moons, were discovered in 1610 by Galileo Galilei and were the first objects found to orbit a body that was neither Earth nor the Sun. From the end of the 19th century, dozens of much smaller Jovian moons have been discovered and have received the names of lovers, conquests, or daughters of the Roman god Jupiter, or his Greek equivalent, Zeus. Eight of Jupiter's moons are regular satellites, with prograde and nearly circular orbits that are not greatly inclined with respect to Jupiter's equatorial plane. The Galilean satellites are spheroidal in shape, and so would be considered dwarf planets if they were in direct orbit about the Sun. The other four regular satellites are much smaller and closer to Jupiter; these serve as sources of the dust that makes up Jupiter's rings. Jupiter's other 54 or 55 moons are tiny irregular satellites, whose prograde and retrograde orbits are much farther from Jupiter and have high inclinations and eccentricities. These moons were likely captured by Jupiter from solar orbits. There are 13 recently-discovered irregular satellites that have not yet been named, plus a 14th whose orbit has not yet been established. Characteristics The moons' physical and orbital characteristics vary widely. The four Galileans are all over 3000 km in diameter; the largest Galilean, Ganymede, is the largest object in the Solar System outside the Sun and the eight planets. All other Jovian moons are less than 250 km in diameter, with most barely exceeding five km. Even Europa, the smallest of the Galileans, is five thousand times more massive than all the non-Galilean moons combined. Orbital shapes range from nearly perfectly circular to highly eccentric and inclined, and many revolve in the direction opposite to Jupiter's spin (retrograde motion). Orbital periods range from seven hours (taking less time than Jupiter does to spin around its axis), to some 3000 times more (almost three Earth years). Origin and evolution Jupiter's regular satellites are believed to have formed from a circumplanetary disk, a ring of accreting gas and solid debris analogous to a protoplanetary disk. They may be the remnants of a score of Galilean-mass satellites that formed early in Jupiter's history. Simulations suggest that, while the disk had a relatively low mass at any given moment, over time a substantial fraction (several tens of a percent) of the mass of Jupiter captured from the Solar nebula was processed through it. However, the disk mass of only 2% that of Jupiter is required to explain the existing satellites. Thus there may have been several generations of Galilean-mass satellites in Jupiter's early history. Each generation of moons would have spiraled into Jupiter, due to drag from the disk, with new moons then forming from the new debris captured from the Solar nebula. By the time the present (possibly fifth) generation formed, the disk had thinned out to the point that it no longer greatly interfered with the moons' orbits. The current Galilean moons were still affected, falling into and being partially protected by an orbital resonance which still exists for Io, Europa, and Ganymede. Ganymede's larger mass means that it would have migrated inward at a faster rate than Europa or Io. The outer, irregular moons are thought to have originated from passing asteroids while the protolunar disk was still massive enough to absorb much of their momentum and thus capture them into orbit. Many broke up by the stresses of capture, or afterward by collisions with other small bodies, producing the families we see today. Discovery , Europa, Ganymede, Callisto.]] The first claimed observation of one of Jupiter's moons is that of the Chinese astronomer Gan De around 364 BC. However, the first certain observations of Jupiter's satellites were those of Galileo Galilei in 1609. By March 1610, he had sighted the four massive Galilean moons with his 30x magnification telescope: Ganymede, Callisto, Io, and Europa. No additional satellites were discovered until E.E. Barnard observed Amalthea in 1892. With the aid of telescopic photography, further discoveries followed quickly over the course of the twentieth century. Himalia was discovered in 1904, Elara in 1905, Pasiphaë in 1908, Sinope in 1914, Lysithea and Carme in 1938, Ananke in 1951, and Leda in 1974. By the time Voyager space probes reached Jupiter around 1979, 13 moons had been discovered, while Themisto was observed in 1975, but due to insufficient initial observation data, it was lost until 2000. The Voyager missions discovered an additional three inner moons in 1979: Metis, Adrastea, and Thebe. For two decades no additional moons were discovered; but between October 1999 and February 2003, researchers using sensitive ground-based detectors found another 32 moons, most of which were discovered by a team led by Scott S. Sheppard and David C. Jewitt. These are tiny moons, in long, eccentric, generally retrograde orbits, and average of in diameter, with the largest being just across. All of these moons are thought to be captured asteroidal or perhaps cometary bodies, possibly fragmented into several pieces, but very little is actually known about them. A number of 14 additional moons were discovered since then, but not yet confirmed, bringing the total number of observed moons of Jupiter at 63. As of 2008, this is the most of any planet in the Solar System, but additional undiscovered, tiny moons may exist. Naming The Galilean moons of Jupiter (Io, Europa, Ganymede and Callisto) were named by Simon Marius soon after their discovery in 1610. However, until the 20th century these fell out of favor, and instead they were referred to in the astronomical literature simply as "Jupiter I", "Jupiter II", etc., or as "the first satellite of Jupiter", "Jupiter's second satellite", and so on. The names Io, Europa, Ganymede, and Callisto became popular in the 20th century, while the rest of the moons, usually numbered in Roman numerals V (5) through XII (12), remained unnamed. By a popular though unofficial convention, Jupiter V, discovered in 1892, was given the name Amalthea, first used by the French astronomer Camille Flammarion. The other moons, in the majority of astronomical literature, were simply labeled by their Roman numeral (i.e. Jupiter IX) until the 1970s. In 1975, the International Astronomical Union's (IAU) "Task Group for Outer Solar System Nomenclature" granted names to satellites V–XIII, and provided for a formal naming process for future satellites to be discovered. The practice was to name that newly discovered moons of Jupiter after lovers and favorites of the god Jupiter (Zeus), and since 2004, after their descendants also. All of Jupiter's satellites from XXXIV (Euporie) are named after daughters of Jupiter or Zeus. Some asteroids share the same names as moons of Jupiter: 9 Metis, 38 Leda, 52 Europa, 85 Io, 113 Amalthea, 239 Adrastea. Two more asteroids previously shared the names of Jovian moons until spelling differences were made permanent by the IAU: Ganymede and asteroid 1036 Ganymed; and Callisto and asteroid 204 Kallisto. Groups (the horizontal axis in Gm); by orbital inclination (the vertical axis); and orbital eccentricity (the yellow lines). The relative sizes are indicated by the circles.]] Regular satellites These are split into two groups: :*'Inner satellites' or Amalthea group—they orbit very close to Jupiter: Metis, Adrastea, Amalthea, and Thebe. The innermost two orbit in less than a Jovian day, while the latter two are respectively the fifth and seventh largest moons in the Jovian system. Observations suggest that at least the largest member, Amalthea, did not form on the present orbit, but that it was formed farther from the planet, or that it is a captured Solar System body. These moons, along with a number of as-yet-unseen inner moonlets, replenish and maintain Jupiter's faint ring system. Metis and Adrastea help to maintain Jupiter's main ring, while Amalthea and Thebe each maintain their own faint outer rings. :*'Main group' or Galilean moons—the four massive satellites: Ganymede, Callisto, Io, and Europa. With radii that are larger than any of the dwarf planets, they are some of the largest objects in the Solar System outside the Sun and the eight planets in terms of diameter. Respectively the first, third, fourth, and sixth largest natural satellites in the Solar System, they contain almost 99.999% of the total mass in orbit around Jupiter. Jupiter is about five thousand times more massive than the Galilean moons. kg / Mass of Galilean moons 3.93 kg = 4,828|group=note|name=Big4Mass}} The inner moons also participate in a 1:2:4 orbital resonance. Models suggest that they formed by slow accretion in the low-density Jovian subnebula—a disc of the gas and dust that existed around Jupiter after its formation—which lasted up to 10 million years in the case of Callisto. Irregular satellites The irregular satellites are substantially smaller objects with more distant and eccentric orbits. They form families with shared similarities in orbit (semi-major axis, inclination, eccentricity) and composition; it is believed that these are at least partially collisional families that were created when larger (but still small) parent bodies were shattered by impacts from asteroids captured by Jupiter's gravitational field. These families bear the names of their largest members. The identification of satellite families is tentative, but the following are typically listed: * Prograde satellites: :*Themisto is the innermost irregular moon and not part of a known family. :*The Himalia group is spread over barely 1.4 Gm in semi-major axis, 1.6° in inclination (27.5 ± 0.8°), and eccentricities between 0.11 and 0.25. It has been suggested that the group could be a remnant of the break-up of an asteroid from the main asteroid belt. :*Carpo is the outermost prograde moon and not part of a known family. * The irregular retrograde satellites are thought to have originally been asteroids that were captured by drag from the tenuous outer regions of Jupiter's accretion disk while the Solar system was still forming, and were later shattered by impacts. They are far enough from Jupiter that their orbits are significantly disturbed by the gravitational field of the Sun. :*S/2003 J 12 is the innermost of the retrograde moons, and is not part of a known family. :*The Carme group is spread over only 1.2 Gm in semi-major axis, 1.6° in inclination (165.7 ± 0.8°), and eccentricities between 0.23 and 0.27. It is very homogeneous in color (light red) and is believed to have originated from a D-type asteroid progenitor, possibly a Jupiter trojan. :*The Ananke group has a relatively wider spread than the previous groups, over 2.4 Gm in semi-major axis, 8.1° in inclination (between 145.7° and 154.8°), and eccentricities between 0.02 and 0.28. Most of the members appear gray, and are believed to have formed from the breakup of a captured asteroid. :*The Pasiphae group is quite dispersed, with a spread over 1.3 Gm, inclinations between 144.5° and 158.3°, and their eccentricities between 0.25 and 0.43. The colors also vary significantly, from red to grey, which might be the result of multiple collisions. Sinope, sometimes included into Pasiphae group, is red and given the difference in inclination, it could have been captured independently; Pasiphae and Sinope are also trapped in secular resonances with Jupiter. :*S/2003 J 2 is the outermost moon of Jupiter, and is not part of a known family. Table The moons of Jupiter are listed below by orbital period. Moons massive enough for their surfaces to have collapsed into a spheroid are highlighted in bold. These are the four Galilean moons, which are comparable in size to Earth's Moon. The four inner moons are much smaller. The irregular captured moons are shaded light gray when prograde and dark gray when retrograde. See also * Galilean moons * Jupiter's moons in fiction * Rings of Jupiter * Natural satellites of Earth · Mars · Saturn · Uranus · Neptune Notes References External links * Jupiter's Moons by NASA's Solar System Exploration * "43 more moons orbiting Jupiter" article appeared in 2003 in the San Francisco Chronicle * Articles on the Jupiter System in Planetary Science Research Discoveries * An animation of the Jovian system of moons Category:Moons of Jupiter Category:Lists of moons als:Liste der Jupitermonde ast:Satélites de Xúpiter be-x-old:Спадарожнікі Юпітэра bs:Jupiterovi prirodni sateliti br:Loarennoù Yaou bg:Естествени спътници на Юпитер ca:Satèl·lits de Júpiter cs:Měsíce Jupiteru da:Jupiters måner de:Liste der Jupitermonde el:Δορυφόροι του Δία es:Satélites de Júpiter eo:Listo da jupiteraj lunoj eu:Jupiterren satelite fa:فهرست ماه‌های مشتری fr:Satellites naturels de Jupiter ko:목성의 위성 hr:Jupiterovi prirodni sateliti ilo:Bulbulan iti Jupiter it:Satelliti naturali di Giove ka:იუპიტერის ბუნებრივი თანამგზავრები lv:Jupitera pavadoņi lb:Jupitermounden lt:Jupiterio palydovai nah:Huēyitzitzimicītlalli īmētz nl:Lijst van manen van Jupiter ja:木星の衛星と環 no:Jupiters måner nn:Jupitermånane nds:List von de Jupiter-Maanden pl:Lista naturalnych satelitów Jowisza pt:Satélites naturais de Júpiter ro:Sateliţii naturali ai lui Jupiter ru:Спутники Юпитера simple:List of Jupiter's moons sk:Mesiace Jupitera sl:Jupitrovi naravni sateliti sr:Јупитерови природни сателити sh:Jupiterovi prirodni sateliti fi:Jupiterin kuut sv:Jupiters naturliga satelliter th:ดวงจันทร์ของดาวพฤหัสบดี tg:Радифҳои Муштарӣ tr:Jüpiter'in doğal uyduları uk:Супутники Юпітера zh:木星的卫星